The present invention relates to a honeycomb structure, and to a method for manufacturing the honeycomb structure.
In recent years, environmental considerations have increased the necessity for removing particulate matter in exhaust gases from combustion apparatuses, such as internal combustion engines and boilers. In particular, regulations relating to removal of particulate matter (PM) including graphite particles discharged from diesel engines are being strengthened in Europe, the United States, and Japan. A honeycomb structure referred to as a diesel particulate filter (DPF) has been used as a filter for capturing and removing substances such as PM. A honeycomb structure is accommodated in a casing that is arranged in an exhaust passage of a combustion apparatus. The honeycomb structure has a large number of cells that extend in the longitudinal direction of the structure. The cells are partitioned by partitions. In every pair of adjacent cells, one cell has an open end on one side and the other cell has an open end on the opposite side. The open end of one cell and the open end of the other cell are sealed by a plug. Plugs are arranged in a lattice on each end surface (inlet side end surface and outlet side end surface) of the honeycomb structure. Exhaust gas enters open cells at the inlet side end surface of the honeycomb structure, flows through the porous partitions, and is discharged from adjacent open cells at the outlet side end surface. For example, PM discharged from a diesel engine is captured by the partitions that function as a particle capturing filter, and accumulates on the partitions. The PM accumulating on the partitions is burned and removed by a heating means, such as a burner or a heater, or by heat from the exhaust gas.
WO 2003/067041A describes a ceramic structure that is formed by joining a plurality of porous ceramic members with a bonding agent. The outer surface of the ceramic structure is coated by a coating layer for preventing leakage of exhaust gas. The coating layer is formed by hardening a coating agent containing inorganic fibers such as silica-alumina fibers (10 to 70 mass %), inorganic particles such as silicon carbide (3 to 80 mass %), an inorganic binder such as a silica sol (1 to 15 mass %), and an organic binder such as carboxymethyl cellulose (0.1 to 5 mass %).
WO 2005/047209A describes a honeycomb structure using a coating agent containing a particulate filler in addition to ceramics as its main component.
The entire contents of WO 2003/067041A and WO 2005/047209A are incorporated herein by reference.